The present invention relates to a vacuum cleaner system using an electrostatically charged bag and a bag suitable for use therein.
A conventional vacuum cleaner includes a hollow air inlet, an air outlet, a removable dust bag communicating with the inlet and the outlet, and means for moving initially dirt-laden air from the inlet to the outlet via the bag so that the dirt remains trapped within the bag. Modern dust bags are typically disposable 2-ply dust bags comprised of an inner ply of highly air-permeable material and a conventional outer ply of air-permeable material. The inner or filter ply is actually a non-woven liner formed of randomly intertangled discontinuous microfibers of synthetic material and assists in the trapping of smaller dirt particles within the bag.
It has recently been found to be advantageous to charge the dust bag--and in particular the non-woven liner of a 2-ply dust bag--with an electrostatic charge. As many of the smaller dust particles typically naturally contain a negative charge, the use of a negatively charged bag causes the bag to repel the approach of the negatively charged dust particles and thus maintains the dust particles within the bag. By increasing this type of "magnetic filtration," one does not have to rely as much on the mechanical filtration characteristics (that is, the permeability) of the dust bag because the charge on the dust bag supplements the low permeability of the dust bag in trapping dust particles. This permits the bag to be significantly more porous, and thereby reduces the pressure drop differential resulting from the air passing through the bag. Accordingly, there is a greater air flow through the bag as a result of the same pressure drop. Increased vacuum cleaner cleanability and increased bag fill capacity typically result.
Thus, electrostatically charged dust bags (and especially 2-ply vacuum cleaner dust bags with an electrostatically charged inner ply) are commercially available. Typically, during the manufacture of the inner ply fabric, the fabric is corona treated to create the electrostatic charge thereon. The electrostatically charged fabric is then used in the manufacture of a 2-ply vacuum cleaner dust bag, which is then sold to end users for use in vacuum cleaners. The problem with prior art electrostatically charged dust bags is the fact that the electrostatic charge tends to bleed away rapidly over time. Further, these dust bags are more expensive to manufacture because of the extra step of corona treatment. Thus, a significant portion of the charge is typically lost with a concomitant loss in cleaning power. As a result, manufacturers of electrostatically charged dust bags must still rely primarily on the mechanical filtration characteristics of the bag.
Accordingly, it is an object of the present invention to provide a vacuum cleaner system wherein the leakage of electrostatic charge from the dust bag does not adversely affect operation of the vacuum cleaner.
Another object is to provide such a system which does not require protection of the dust bag from moisture at any time.
A further object is to provide such a system which in one embodiment enables the user of the system to decide whether or not to employ an electrostatically charged dust bag.
It is also an object of the present invention to provide such a system which in one embodiment increases the efficacy of the magnetic filtration characteristics of an electrostatically charged dust bag or imparts magnetic filtration characteristics to an uncharged dust bag.
It is another object to provide dust bags suitable for use in such a system.